I have a mix of Debian and Ubuntu machines. A laptop for software development, servers, and a home theater PC. I started out on Debian, switched to Ubuntu a few years ago, and am migrating back to Debian due to an increasing number of Ubuntu policies that annoy me (Unity, Amazon integration, removing legacy video drivers, Mir, etc.). I've also used FreeBSD and OpenBSD for a few things and am considering migrating to PC-BSD/FreeBSD since I like their release schedule and licensing better.
I started out using Linux because Unix-based OSs were just technically superior for software development vs. the Windows 9x and MacOS 8 alternatives that were available at the time. I stayed because I'm cheap and I appreciate the ideals of the FOSS community.